Stamping faces of ink-containing stamp devices and ink penetration seals are formed by porous stamp materials including interconnected cells. Generally, vulcanized rubber, such as NBR (nitrile rubber), and thermosetting resins are used as a porous stamp material. Japanese Unexamined Patent Application Publication No. 2000-006509 and Japanese Unexamined Patent Application Publication No. 2000-335068 state that a thermoplastic resin is used for a stamp material. Some thermoplastic resins having cross linking agents added to improve heat resistance are also known. When a vulcanized rubber, a thermosetting resin, or a thermoplastic resin having a cross linking agent added is used as a stamp material, a press molding method is usually adopted for manufacture of a stamp. When a non-cross linked thermoplastic resin is used for a stamp, an extrusion molding method can be adopted for manufacture of a stamp.
As a means to form a desired stamping face (an imprint of a stamp) on the surface of the stamp made from porous stamp materials, a laser beam irradiation processing has been conventionally performed. Vulcanized rubber materials, such as NBR, enable high-precision laser processing, but emit an unpleasant smell at the time of processing, and thus require attachment of an air exhauster to a processing equipment. It is also required that the stamping face should be washed, because residues adhere on the stamping face after processing.
Porous stamp material made from thermoplastic resin without a cross linking agent enables extrusion molding, but is not appropriate for laser processing. This is because not only resins on laser beam-irradiated parts but also their surroundings melt before they burn and evaporate, and thus it is not possible to form a stamping face with sharp edge (well-defined outline) using such a porous stamp material. An imprint of an ink-containing stamp device made with such a stamp has thinner lines than required and blurs its outline. Moreover, melting of the stamp material by laser radiation could possibly cause clogging phenomena in the stamp.
Japanese Unexamined Patent Application Publication No. 2002-361992 states a technique that enables laser processing of a thermoplastic resin as a stamp material. The technique in Japanese Unexamined Patent Application Publication No. 2002-361992 enables conventional laser processing by previously absorbing liquid substances such as water in a porous stamp material mainly comprising a thermoplastic material in the manufacture of a stamp by laser processing.
The porous stamp material described in Japanese Unexamined Patent Application Publication No. 2002-361992 comprises a 20 or more percent by mass of thermoplastic material, a rubber-like elastic substance, and a small amount of a vulcanizing agent as components. The thermoplastic material is thermoplastic resin or thermoplastic elastomer. The liquid substance absorbed in the porous stamp material is water, glycerol, ethylene glycol, propylene glycol, methyl alcohol, ethyl alcohol, and water based ink comprising water as a main component, or the like.
The technique described in Japanese Unexamined Patent Application Publication No. 2002-361992 solve the problem, which is a defect in formation of an imprint caused by the thermoplastic material affected by heat propagation at the time of laser processing, by previously absorbing in the porous stamp material the liquid substance such as water. The document also states significant effects that this technique enables conventional laser processing for the stamp material made from thermoplastic resin, resulting in a sharp imprint while generating no unpleasant smell at the time of laser processing, and leaves no laser processing residues on stamping face with the residues being taken up into the melted thermoplastic material, requiring no need for washing after the processing and resulting favorable stamping face condition.